The present invention relates to electrical generators driven by aircraft engines, and more particularly, to protection systems for preventing damage to aircraft engine gearboxes and generators.
A typical aircraft generates on-board electrical power by utilizing auxiliary power from its engines. The engines have a take-off shaft that goes through a gearbox and then to an electric generator to produce electricity for the aircraft.
If for some reason the temperature in an electric generator is suddenly higher or lower than normal or if any other abnormality occurs, like bearing failure or winding shorts, there is a need to discontinue driving the generator so that damage to the generator and/or the engine gearbox is precluded or at least minimized. Such disconnection may occur through operation of a shear section in generator driver shaft. The shear section is designed such that the increased torque will eventually shear the shaft resulting in an interruption of power being transmitted from the jet engine gearbox to the generator.
Many newer aircraft now employ variable speed, variable frequency or DC generators. A significant issue with variable speed generators is that the shaft shear section needs to be sized for minimum speed, maximum load operation. When variable speed generators are running at high speed, drive torque is much reduced for the same maximum load power. So at high speed the rotating energy to operate (i.e., break) the shear section can be very high, leading to high vibration and consequential damage.
As can be seen, there is a need for an externally operable disconnect. Additionally it is desirable that the disconnect be resettable so it can be periodically tested and then reset.